1. Field of the Invention
The present invention relates to position sensing in the Z-axis direction. More particularly, the present invention relates to an optical sensor capable of continuously monitoring the Z-axis position of a tool such as a pick-up tool with or without a component mounted on the tool.
2. Description of the Prior Art
Heretofore, optical micrometers have been employed to measure or gauge dimensions or parts without physically touching the part being measured. Optical sensors have also been employed to sense the size and relative position of a component after being picked up by a pick-up tool from a supply point or feeder station.
Even though the tip of the pick-up tool or the lower extremity of a component mounted on a pick-up tool is determinable by employing prior art optical sensors, the same sensor has not heretofore been employed to sense the Z-axis position of a pick-up tool as it is engaging a substrate or a component at the time of pick-up or at the time of engagement of the component with a substrate when it is being mounted or bonding onto a carrier.
Z-axis position of the top of a component, the Z-axis position of the top surfaces of the workpiece and the reference and/or datum points on a pick and place machine are not presently available without employing test instrument sensing devices.
Heretofore, pick and place machines and die attach machines (die bonders) have been provided with separate systems for sensing touch down of the tool. One type system monitors the electrical characteristics of the Z-servo drive system and/or electrical characteristics of the ultrasonic transducer and determines when a change in electrical characteristics occur that are indicative of a touchdown position. Such systems are often a part of wire bonder monitoring systems. Die bonders and pick and place machines usually employ a dedicated sensor or sensors for determining the Z-position of the bottom of a component and/or the Z-position of the substrate. Such systems may employ a plurality of sensors, none of which are fixed on or carried with the transport structure supporting the pick-up tool.
Accordingly, it would be desirable to provide in a pick and place machine or a die bonder, and other types of machines using pick-up tools, a simple and accurate optical sensor capable of determining the Z-position of reference surfaces on the machine, and/or the touch down position of the components carried by the pick-up tool.